An enhanced threshold-based feedback scheme for massive MU-MIMO downlink FDD systems

In this paper, we propose an enhanced threshold- based feedback strategy for massive multiuser multiple-input multiple-output (MU-MIMO) downlink systems adopting two- stage beamforming. The key idea lies in checking the degree of alignment with fixed beamforming vectors at user terminal (UT) by utilizing the effective channel and average inter-group interference-plus-noise power (IGINP). Subsequently, the UT determines whether UT feeds back the channel quality indicator (CQI) pair to base station (BS) or not, thereby reducing the amount of feedback overhead. Numerical results show that the proposed scheme effectively reduces the number of feedback users while the sum rate is maintained compared to conventional feedback strategy.